Detection of an artificial defect and influence of sand on the damping of a pressure pulse in a pipeline section
The project is targeted to develop a scheme for non-intrusive detection of flaws in metal pipelines. In the laboratory, experiments were conducted on a steel pipeline section. The generation and detection of the acoustic pulse is non-intrusive and can be performed with just an electrical contact of the pipe. Acoustic pulses are generated by a pulsed magnetic field. In the investigation, the magnetic pressure in a coil generates the acoustic pulses. The pulses propagate in either direction along the pipe. A detector picks up these acoustic pulses and any reflected pulses. Reflections are caused from the ends of the metal pipeline section as well as any imperfections and/or discontinuities, like thin spots due to corrosion in the pipeline. The pressure pulse causes a temporary local change in the diameter of the pipe, leading to a voltage change of the charged electrode of the detector. The reflections recorded by the detector on the oscilloscope indicate existence and, from the time delay, the location of any defect. Reflected pulses from thin areas, with a longitudinal extension of about one pipe radius and a reduction of the wall thickness of 40% were detected clearly. The attenuation of the pulses for pipes buried in sand was also studied. Measurements were done with varying sand depths. The length of sections of pipeline that can be checked with this pulse-echo method is about 14 m, or 7 m in both directions, for pipelines buried under 3 feet of sand. Experimental results are presented.